Yes, you can take inositol with levothyroxine. No studies have identified a direct chemical interaction between the two, and no evidence suggests that inositol interferes with levothyroxine absorption. In fact, research on people with autoimmune thyroid conditions shows that inositol may complement thyroid treatment by lowering TSH levels and reducing thyroid antibodies. That said, combining them does require some awareness of timing and monitoring.
Why the Combination Comes Up
Most people asking this question fall into one of two camps: they have an underactive thyroid (often Hashimoto’s) and heard that inositol supports thyroid function, or they have PCOS and are already taking inositol for insulin and hormone regulation while also needing levothyroxine for their thyroid. Both scenarios are common because thyroid autoimmunity and PCOS frequently overlap.
Myo-inositol, the form used in most research, is a sugar alcohol that acts as a second messenger for several hormones, including TSH. When TSH binds to thyroid cells, inositol helps relay that signal inside the cell through a pathway that triggers calcium release and promotes thyroid hormone production. If inositol levels are low, thyroid cells can become less responsive to TSH, essentially making them “resistant” to the hormone that tells them to work.
What Inositol Does for Thyroid Function
Several clinical trials have tested myo-inositol (combined with selenium) in people with subclinical hypothyroidism or Hashimoto’s thyroiditis. The results are consistent: TSH drops, thyroid antibodies decline, and free thyroid hormone levels nudge upward.
In a trial of 168 people with Hashimoto’s and mildly elevated TSH (between 3 and 6), six months of myo-inositol plus selenium significantly reduced both TSH levels and antibody counts compared to selenium alone. A separate multicenter study of 148 premenopausal women with subclinical hypothyroidism found that six months of supplementation lowered TSH, reduced anti-TPO and anti-thyroglobulin antibodies, improved cholesterol, restored regular menstrual cycles, and eased common hypothyroid symptoms like fatigue, feeling cold, and difficulty losing weight.
In one study published in the International Journal of Endocrinology, TSH dropped from an average of 4.32 to 3.12 over six months. Free T4 rose from 0.94 to 1.07, and free T3 increased slightly as well. Another trial showed TSH falling from a median of 4.7 to 3.8 over six months, with people who started at higher TSH levels seeing the largest drops (from 5.9 down to 4.6).
These are meaningful shifts, particularly for people in the subclinical range where the decision to start or adjust levothyroxine is often uncertain.
No Known Absorption Interference
Levothyroxine is notoriously sensitive to timing. Calcium, iron, antacids, coffee, and certain foods can all block its absorption in the gut. This is why doctors recommend taking it on an empty stomach, typically 30 to 60 minutes before eating. Inositol, however, has not been flagged as an absorption blocker. It works through intracellular signaling pathways rather than binding to levothyroxine in the digestive tract.
Still, a reasonable precaution is to separate the two by at least 30 minutes. Take your levothyroxine first thing in the morning as usual, then take inositol later with a meal or at another time of day. This minimizes any theoretical risk and follows the general principle of keeping levothyroxine isolated from other supplements.
Safety Profile
The combination appears well tolerated. In a study that tracked side effects specifically, the only adverse reaction reported across the entire group was a slight loss of appetite in one participant. Compliance was high, and no signs of hyperthyroidism (which would suggest the combination was pushing thyroid levels too high) were reported. Free T3 and T4 levels remained within normal ranges throughout the trials, even as TSH improved.
The doses used in most thyroid-focused research are 600 mg of myo-inositol combined with 83 micrograms of selenium, taken once or twice daily. This is notably lower than the 2,000 to 4,000 mg doses commonly used in PCOS treatment. If you’re taking higher doses for PCOS, the thyroid effects could potentially be more pronounced, which makes monitoring more important.
Why Monitoring Matters
Because inositol can lower TSH on its own, adding it to levothyroxine creates the possibility that your current dose becomes slightly too strong over time. This wouldn’t happen overnight. The studies show gradual TSH changes over three to six months. But if your thyroid levels are already well controlled on levothyroxine, introducing inositol could shift you from optimal into slightly overtreated territory.
The practical step is to check your thyroid levels (TSH, free T4) about two to three months after starting inositol, then again at six months. If your TSH drops lower than your target range or you develop symptoms like a racing heart, feeling jittery, or trouble sleeping, your levothyroxine dose may need a small reduction. This is a straightforward adjustment, not a sign of a dangerous interaction.
PCOS and Thyroid Overlap
Women with PCOS have higher rates of autoimmune thyroiditis and subclinical hypothyroidism. If you’re in this group, inositol may be addressing both conditions simultaneously: improving insulin sensitivity and ovarian function through one mechanism, and supporting thyroid cell responsiveness through another. A review in Frontiers in Endocrinology noted the favorable effects of myo-inositol on both subclinical hypothyroidism and autoimmune thyroiditis in this population, though the authors emphasized that more targeted data on the levothyroxine-inositol combination in PCOS is still needed.
For now, the available evidence supports using both together with appropriate thyroid monitoring. The key is treating them as complementary rather than redundant. Levothyroxine replaces the thyroid hormone your body isn’t making enough of. Inositol helps your thyroid cells respond better to TSH signaling and may reduce the autoimmune attack driving the problem in the first place. They work through entirely different pathways.